The present invention relates to a numerical control section in a control system for controlling a machine tool or a robot. More particularly, the present invention relates to a numerical control section including a part program and a drive control unit, the latter including at least two control loops for the closed-loop control of the drive systems of the machine tool or robot, and digital-to-analog converters to convert the desired-value and actual-value signals of the control loops to analog signals for use in the control system.
To provide for the accurate positioning of the axes of machine tools or robots, control systems with numerical control systems are designed so that closed-loop control of the actual positions of all axes is performed on the basis of specified desired positions. Such numerical control sections essentially consist of a part program and a drive-control or axis-control unit. The part program contains all information that is necessary for executing a particular machining sequence. It is possible to enter input information into the control system through external data-storage devices, such as a programmer, a magnetic tape or a diskette drive, or manually through a keypad on a control panel. The latter can also be used to enter any other information, such as tool data, correction values and machine setup data. Finally, program data may also be sent to the numerical control system directly from the memory of a production control computer.
The desired values for the drives of the systems to be controlled which have been edited by the part program are routed to the respective control loops of the drive-control unit, which then pass them on, by way of digital-to-analog converters and power output stages which follow, to the drives.
Usually incremental and/or absolute measuring systems which are coupled to the drive systems transmit the actual values back to the control loops from the drive-control unit. The latter thus controls the drives of a machine tool or robot through desired-value versus actual-value comparison.
In addition to the drives to be controlled, machine tools or robots may be equipped with further devices which, while they must perform their function on the basis of operating parameters of the machine tool or robot, do not need to be controlled. Illustrative of such devices are pressure pumps, proportional valves, and electric switches. For example, while a press is being operated, an oil pump must be running constantly to produce a lubricating film for the ram of the press. The fact that the oil pump is being operated might be indicated on a display.
Such further devices thus need to receive only a supply voltage or a digital control signal to perform their function. Up to now, these electric signals either had to be fed in separately by the operator or required the use of additional external hardware such as a stored-program controller or, in the simplest case, a constant-voltage source that might take the form of a battery and a potentiometer, for example.